The present invention relates to an access control card useful in access control systems to permit access to secured areas, secured information, secured systems or the like, and, more particularly, to a battery operated access control card which compares a code generated by a card reader to a first stored code and, if there is a match, for transmitting a second stored code back to the card reader to be used by the card reader to determine whether the holder of the card should be permitted to take the desired action.
Access control systems have been utilized in the past to restrict access to protected areas, information, or the like to only those to whom access is authorized. Such systems usually involve a card reader into which a coded card is inserted and read. The code on the card, which may periodically be changed, may be identical for all those wishing to have access. Alternatively, each person who is authorized to have access may be assigned his own personal code which again may be periodically changed. Upon the recognition of a permissible code, the card reader and associated system will permit access.
These card readers usually comprise a cabinet for housing the access control system or subsystem thereof and typically have a plurality of sensing fingers for making contact with the cards inserted into the reader and for sensing the code on the card to allow access if the card carrier has the proper code. To gain access, the card is inserted into a slot in the cabinet which results in the wiping over of the surface of the card by the sensing fingers during both this insertion and the subsequent withdrawal of the card.
Because these typical prior art card readers involve contact between the reader and the card, there is substantial wear and tear on both the reader and the card which adversely affects the reliability of the overall system. Moreover, since there is direct contact between the reader and the card, and since card readers used in access control systems are quite often located outdoors, certain elements of the card reader, notably the sensing fingers, are exposed to the vagaries of weather and are, therefore, subject to corrosion which again adversely affects the reliability of the system.
The prior art has attempted to solve many of these problems by providing passive cards which either load down a magnetic field which can be then sensed by the generator of the magnetic field to permit access or to receive an RF transmission, code it and return it to the generator of the RF signal to be decoded. An example of this latter approach can be found in U.S. Pat. No. 4,210,900 which shows a surface acoustic wave device for receiving an RF generated signal and for transmitting a coded RF signal in response thereto to a card reader. However, the body capacitance of the users of many types of these passive devices tends to ground the signals being transmitted by the reader so that no useful signal is returned to the reader and access will not be permitted. U.S. Pat. No. 4,210,900 shows one way around this problem by providing a card which can be inserted into a reader but which does not require physical contact with any part of the reader and in which the sensing elements of the reader can be sealed from exposure.